(a) Field of the Invention
The present invention generally relates to a method and apparatus for adjusting hybrid automatic repeat request (HARQ) timing.
(b) Description of the Related Art
A wideband wireless access system, as a next-generation wireless communication scheme, supports a HARQ process in order to ensure high speed data packet transmission, reduce delay, and secure reliability of communication, and adopts a multi-input multi-output (MIMO) technique using multiple transmission antennas and multiple reception antennas in order to improve data transmission/reception efficiency.
According to the HARQ scheme, a receiver decodes a data packet received by a physical layer and determines whether there is an error, and when no error is detected, the receiver transmits an ACK (acknowledgement) signal as a response signal to a transmitter to inform the transmitter about the successful reception of the data packet. Meanwhile, if the receiver detects an error upon decoding the received data packet, the receiver transmits a NACK (negative acknowledgement) signal as a response signal to the transmitter to inform the transmitter about the detected error. Upon receiving the NACK signal, the transmitter may re-transmit a data packet.
A HARQ protocol is classified into a synchronous HARQ and an asynchronous HARQ scheme according to a transmission timing of a retransmission packet. In the synchronous HARQ scheme, transmission timing of a retransmission packet with respect to an initial transmission packet is uniformly fixed, and in the asynchronous HARQ scheme, transmission timing of a retransmission packet with respect to an initial transmission packet is determined by a scheduler of a base station.
The HARQ scheme may also be classified into an adaptive HARQ scheme and a non-adaptive HARQ scheme according to a change in an amount and position of allocated resources. The adaptive HARQ scheme is a scheme of changing an amount and position of allocated resources, and the non-adaptive HARQ scheme is a scheme of fixing an amount and position of allocated resources.
A high scheduling gain and high speed data transmission effect can be obtained by appropriately mixing the synchronous and asynchronous HARQ schemes and the adaptive and non-adaptive HARQ schemes and using small signaling overhead. For example, a mobile communication system may apply the adaptive, asynchronous HARQ to downlink (DL) data transmission, and the synchronous HARQ to uplink (UL) data transmission.
In a wireless communication system, in general, a base station schedules radio resources used in data transmission with respect to uplink and downlink. Here, a transmission time interval (TTI) is used as a transmission time unit. The TTI is a transmission duration of a physical layer with respect to an encoded packet in a radio air interface, which is expressed in the form of a slot or integer number of a subframe. That is, a TTI is a transmission duration of a packet occupying one slot or subframe length, and n TTI is a transmission duration of a subpacket (i.e., a data packet or data burst) by n slots or subframe lengths.
An existing wireless access system follows a scheme in which a HARQ signal is transmitted and received between a base station and a mobile station by using fixed transmission/reception timing irrespective of a radio channel state, characteristics of a service flow (quality of service (QoS), priority, or the like), a HARQ buffer state, or a system load state.
Such fixed transmission/reception timing may implement a simple system but it cannot satisfy QoS of traffic according to characteristics of various services. For example, when real-time traffic such as real-time video streaming or the like, and best effort (BE) traffic such as an e-mail or the like, are mixed, if resource allocation of real-time traffic sensitive to delay is interfered with by a retransmission of BE traffic, QoS will be lowered.
Also, when BE traffic is required to be retransmitted, it may be better for the BE traffic to maintain a more flexible retransmission time in comparison to real-time traffic, in order to provide better priority to the real-time traffic having high priority. Retransmission timing of a service flow having lower priority may be induced to be delayed according to a HARQ buffer state of a mobile station to increase available radio resources, whereby traffic of a service flow having higher priority may be preferentially processed to increase QoS.
Thus, when a mobile station provides various types of traffic simultaneously, packet transmission is required to be controlled according to a radio channel state of the mobile station, characteristics of a service flow, management of a HARQ buffer state, allocation and availability of radio resources, a system load, and the like. A base station is required to effectively use radio resources by controlling traffic transmission/reception timing of each service flow in consideration of a radio channel state, characteristics of a service flow, management of a HARQ buffer state, allocation of radio resources, a system load, and the like.